Tungsten-base alloys



United States Patent 3,307,982 TUNGSTEN-BASE ALLOYS Edward J. Milligan and James C. Kenney, Indianapolis, Ind., assignors to P. R. Mallory & Co., Inc., Indian- "ice sists in heating the alloy to a temperature of 5001200 C. in a neutral or slightly reducing atmosphere, and then quenching it abruptly.

For a sintered compact comprised of 75-99% tungsten,

apolis, Indy a corporation of Delaware balance nickel and copper, the indicated treatment con- .No Drawing. Filed Feb. 17, 1964, Ser. No. 345,087 sists of heating the sintered compact to a temperature 4 Claims. (Cl. 148-133) of 500-1200 C. in a neutral or slightly reducing atmosphere for one-half to twelve hours, quenching rapidly,

ThlS invention PertalIlS t0 tungsten-base alloys and and then reheating to 350-600 C. in a neutral or slightly m ns an me h ds f r impr i g the mechanical P P- 1O reducing atmosphere for one-half to twelve hours and erties of same. quenching.

It is an object of this invention to improve the me- I on-bearing and copper-bearing tungsten-nickel sinchanical properties of sintered tungsten compacts alloyed t d compacts were d using AST (A i 5 with nickel and copper. ciety for Testing Materials) and MPA (Metal Powder Another object is to improve mechanical properties Assn.) standards. The ASTM bar was made by machin- Of sintered tungsten-base compacts alloyed With nickel ing a sintered compactto a reduced diameter of 1A in, and iron. with a 2 in. test length. The MPA test bar was made by Still another object is to effect a selective improvement u ing an MPA die with a reduced area of 0.200" x 0.255 on those compacts exhibiting lowest values of elongation and a test length of 1 in. It will be noted that the ASTM and tensile strength. test bar is approximately 10% greater in area than the Yet another object of this invention is to increase MPA bar and the corresponding difference inmechanical the elongation and tensile strength of the aforementioned properties is shown in Table I.

TABLE I Sintered Only Sintered and Heat-Treated Standard Test Bar Composition Tensile Elongation Tensile Elongation, Heat Strength, p.s.i. Percent Strength, p.s.i. Percent Treat Composition A"=95% W+3.5% Ni+1.5% Cu. Composition B=90% W+7% Ni+3% Fe. Heat Treat a=Heat at 1,200 C. hr., Water quench; reheat to 450 C. 6 hrs., water quench. Heat Treat b=Heat at 1,000 0. 4 hrs. and water quench.

alloys approximately proportionately to the cross-section of the alloy.

Other objects of this invention will become apparent as this invention is explained in detail.

Sintered compacts may be prepared by blending metallic oxides, reducing to a metallic state, compacting in a powder press, and sintering in a reducing atmosphere. Sintered compacts made with about 75% or more tungsten, balance nickel and copper, or nickel and iron, exhibit low ductility in general and even lower ductility for thicker cross-sections. As a consequence, such alloys cannot be swaged, spun, headed or rolled except to a very limited degree, thus reducing the field of potential applications of such sintered compacts.

It has been found that a specific heat-treatment may be applied to the iron-bearing and copper-bearing nickeltungsten compositions, that has the effect of greatly increasing the elongation and appreciably increasing the tensile strength. Furthermore, the percentage increase is greater for thick sections than for ,thin section, thus tending to produce parts of relatively uniform properties despite a non-uniform cross-section.

An efiective heat treatment for a sintered compact comprised of 75-99% tungsten, balance nickel and iron, con- Comparing the MPA and ASTM test bars as sintered, it is seen that the MPA bar is about 10% stronger and 40% more ductile than the ASTM bar, attributable to the dilference in cross-section of the two bars.

The effect of heat treatment b on the ASTM bar is an increase in tensile strength of 45% and an increase in elongation of 450%. Note that these values are greater than obtained with the MPA bar which has a tensile strength of 106,000 p.s.i. and elongation of 4-6% as sintered and a tensile strength of 125,000 p.s.i. and an elongation of 1525% after the stipulated heat treatment b. This corresponds to an improvement of 18% in tensile strength and 300% in elongation and illustrates quite well that the trend of the stipulated heat treatment is more effective on sintered compacts of lower tensile strength and elongation than on sintered compacts closer to the ultimate values. This effect tends to produce a more uniform product after such heat treatment.

Another composition referred to in Table I as Composition A and comprised of tungsten, 3.5% nickel, and 1.5% copper was made into an MPA test bar and exhibited a tensile strength of 118,000 p.s.i. and elongation of 7% after sintering and a tensile strength of 132,000 p.s.i. and elongation of 15% after heat treatment a, thus proving the validity of the heat treatment stipulated.

As the elongation is on the order of 15%, the sintered compacts, so treated, are capable of being rolled swaged, spun, headed and formed, thus being applicable to many products where reliable, economical attachment is required and where maximum tensile strength is indicated.

Now that the invention has been revealed completely, the following claims are made:

1. In a process for heattreating an alloy consisting of 75-99% tungsten, balance nickel and copper, the steps of heating the alloy to a temperature of 5001200 C. in a neutral atmosphere, quenching rapidly, reheating to a temperature of 350600 C. in a substantially neutral atmosphere for one-half to twelve hours and quenching, to increase elongation and tensile strength.

2. An alloy comprised of about 95% tungsten, 3.5% nickel, balance copper having a grain structure and inner granular composition for providing an elongation of substantially about 15% and tensile strength of substantially about 132,000 p.s.i.

3. A process for heat-treating an article of manufacture having a non-uniform cross-section and consisting of 7599% tungsten, balance nickel and copper, the steps of heating said article uniformly to a temperature of 500-1200 C. in a slightly reducing atmosphere, quenching rapidly, reheating to a temperature of 350-600" C.

References Cited by the Examiner UNITED STATES PATENTS 2,655,457 10/1953 Verdi 148l33 X 2,793,951 5/1957 Green et al. 75-176 X FOREIGN PATENTS 160,568 l/1955 Australia.

OTHER REFERENCES The Journal of the Institute of Metals, vol. 57, No. 1, 1938, pages 239 and 240.

DAVID L. RECK, Primary Examiner.

C. N. LOVELL, Assistant Examiner. 

1. IN A PROCESS FOR HEAT-TREATING AN ALLOY CONSISTING OF 75-99% TUGSTEN, BALANCE NICKEL AND COPPER, THE STEPS OF HEATING THE ALLOY TO A TEMPERATURE OF 500-1200*C. IN A NEUTRAL ATMOSPHERE, QUENCHING RAPIDLY, REHEATING TO A TEMPERATURE OF 350-600*C. IN A SUBSTANTIALLY NEUTRAL ATMOSPHERE OF ONE-HALF TO TWELVE HOURS AND QUENCHING, TO INCREASE ELONGATION AND TENSILE STRENGTH. 